/* Write a function named first_non_repeating_letter that takes a string input,
and returns the first character that is not repeated anywhere in the string.

For example, if given the input 'stress', the function should return 't', since
the letter t only occurs once in the string, and occurs first in the string.

As an added challenge, upper- and lowercase letters are considered the same
character, but the function should return the correct case for the initial
letter. For example, the input 'sTreSS' should return 'T'.

If a string contains all repeating characters, it should return an empty string
("") or None -- see sample tests.  */

const initialData = 'sTress'; // T

function firstNonRepeatingLetter(s) {
	const text = s.toLowerCase();
	for (let i = 0; i < text.length; i++)
		if(text.indexOf(text[i]) === text.lastIndexOf(text[i])) {
			return s[i];
		}

	return "";
}

console.log(firstNonRepeatingLetter(initialData));
